1. Field of the Invention
The present invention relates generally to an antenna, and more particularly, pertains to a vertical antenna.
2. Description of the Prior Art
Those concerned with antennas have long recognized the need for a vertical antenna of manageable physical size yielding a desirable gain. The present invention fullfills this need.
In the field of vertical antennas, especially VHF and UHF antennas, it has been a general practice to utilize phase reversal stubs or self-cancelling coaxial sections making instantaneous current flow take the same direction along the entire vertical radiator or along as much of the radiator as possible. The phase reversal stubs have been unsatisfactory in that the vertical radiator has to be broken with insulating material at or near the inner current antinodes. Since the inner current antinodes are high voltage points, losses are apt to be severe, especially in damp weather and even with the best insulating materials available. Another objection is the weight of the insulators as the phasing reversal stubs have to be self-supporting tubing or rod, or encompassed within self-supporting tubing or rod. A further objection has to do with the additional manufacturing steps involved in manufacturing vertical antennas with the phase reversal stubs including the additional manufacturing expense.
Phase reversal sections can also be quarter wave closed transmission line stubs. The stubs provide that currents in adjacent radiating sections will be in phase with no major or minor high angle lobes. Other phase reversal sections can be in the form of coaxial sections which are mechanically connected to the vertical antenna and results in a system which is electrically and mechanically complicated. A further type of phase reversal section is different lengths of transmission lines interconnecting a number of vertical dipoles together.
One prior art antenna utilizes an extended double zepp section which has been published in a majority of the electrical and antenna handbooks for at least over the last half century. This antenna spaces out the high current points on two five-eighths wavelength collinear radiators in order to approach a gain figure of three collinear half wave elements. The vertical radiator is split in only one place at a low voltage point and a phase reversal stub is utilized which is one-eighth wavelength long. The antenna appears to be an electrical equivalent of a quarter wave stub along where the feed line is tapped for lowest SWR and which is a variation of the old J-match.
The present invention provides a vertical antenna that overcomes all the disadvantages of the prior art vertical antennas and provides a realizable gain which is theoretically greater than comparable vertical antennnas.